An individual human immunodeficiency virus type 1 (HIV-1) can be observed in three dimensions using optical tweezers that trap the virus contact-free in culture fluid, reports a study published online in Nature Nanotechnology this week. The findings show that individual HIV-1 virions differ in the number of envelope proteins, which implies substantial heterogeneity in their transmission and infection.

Optical tweezers use the momentum of light photons to trap and manipulate microscopic objects without physically contacting them. This allows for observation of the objects under native conditions. However, previous studies have not been able to trap single animal viruses due to technical and biosafety issues.

Wei Cheng and colleagues created a technique that uses ultrahigh-resolution optical tweezers to trap HIV-1 virions. They report that individual HIV-1 virions differ in the numbers of envelope proteins - important for helping the virus enter host cells - by more than one order of magnitude.